Method and device for operating at least one turbocharger on an internal combustion engine

ABSTRACT

A method and a device for operating at least one supercharger of an internal combustion engine is described, the actuating signal for at least one actuating element of the supercharger (waste gate actuator, electrical auxiliary compressor) being generated as a function of the exhaust gas volume flow in the exhaust tract of the internal combustion engine.

FIELD OF THE INVENTION

The present invention relates to a method and a device for operating atleast one supercharger of an internal combustion engine.

BACKGROUND INFORMATION

Exhaust gas turbochargers are used in some applications for increasingthe power output of engines. The volume flow of exhaust gas drives aturbine connected via a shaft to a compressor which compresses theintake air. The compression ratio is a function of the volume flow ofthe gas passing through the turbine. The exhaust gas turbocharger inexisting approaches is designed so that high compression occurs, even atlow gas flow rates. So that compression ratios and turbine rotationalspeeds that could damage the engine or exhaust gas turbocharger do notresult at high gas throughput rates, a bypass around the turbine, knownas a “waste gate,” is installed. A flap or valve is provided in thisbypass which modifies the cross section of the bypass opening. In oneknown approach, the flap or valve is actuated by a linkage which ismoved by an aneroid capsule. The diaphragm of the capsule is connectedto the linkage. A spring in the capsule forces the diaphragm upward. Theboost pressure which is supplied from the intake manifold via a hosepipe of the aneroid capsule acts against the spring force. At high boostpressures the boost pressure prevails, and the waste gate opens. Thissystem acts as a mechanical-pneumatic regulation. Depending on the gasvolume flow, specified boost pressures are established in the intakemanifold. To enable the boost pressure to be varied independently fromthese physical factors, a timing valve is installed in the hose pipeleading to the aneroid capsule. The function of the boost pressureregulation is to actuate this timing valve in such a way that anintended boost pressure is established. As the timing ratio increases,increasingly more air is discharged from the hose pipe to the outside.As a result, the back pressure against the spring drops, the waste gatecloses, and the boost pressure rises (see, for example, Bosch,Automotive Handbook, 3rd edition, pages 466-71).

It has been shown that other adjustment mechanisms for controlling thecross section of the bypass opening may also be used, such as actuationof the linkage of the flap by an electrical actuator. The pneumaticcounter-coupling over the boost pressure, which makes the exhaust gasturbocharger inherently stable, is thus omitted. The pneumaticcounter-coupling enlarges the cross section of the opening as the boostpressure increases, thereby preventing the turbine from overspeeding.Without pneumatic counter-coupling the exhaust gas turbocharger isco-coupling, and therefore unstable. Other adjustment mechanismsinclude, for example, a variable turbine geometry, a variable slidingturbine, or a valve in the waste gate which is moved by a servomotor.The counter-coupling characteristic is at least partially absent forthese actuators as well. Therefore, there is a need for a boost pressureregulation which is universally applicable and which ensures thestability of the exhaust gas turbocharger.

Another consideration is that an electrical compressor is installed inseries to improve the response characteristics of an exhaust gasturbocharger. This is set, for example, below a specified enginerotational speed when the driver requests acceleration (see, forexample, U.S. Pat. No. 6,029,452). Boost pressure regulation should alsobe usable in such a system.

SUMMARY OF THE INVENTION

By controlling the supercharger system as a function of the exhaust gasvolume flow, the controllability of an exhaust gas turbocharger systemin terms of control engineering is ensured by electronic boost pressureregulation. Thus, the same regulating algorithm may advantageously beused for different types of actuators. This is because thecounter-coupling characteristics, absent when other actuators are usedon the exhaust gas turbocharger, are simulated by setting up anelectrical pilot control of the actuator as a function of the exhaustgas volume flow. Thus, damage to the supercharger system by theapplication of boost pressure regulating parameters is also effectivelyprevented.

The above-mentioned advantages are also achieved when an electricalsupercharger system, in particular an electrical auxiliary charger, isused in conjunction with an exhaust gas turbocharger. Here as well, thecounter-coupling response is simulated by the pilot control as afunction of the exhaust gas volume flow.

The start time and the duration of the electrical auxiliary compressor'soperation are advantageously derived on the basis of the exhaust gasvolume flow by running the auxiliary compressor only until the exhaustgas volume flow reaches the volume flow demand of the turbine. In thismanner the operating time of the electrical auxiliary compressor, andthus the load on the battery, is advantageously minimized.

It is also advantageous that the auxiliary compressor is not switched onunless a setpoint boost pressure is required which exceeds the baseboost pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general diagram of an internal combustion engine havingan exhaust gas turbocharger.

FIG. 2 shows a flow chart of a control of the internal combustionengine.

FIG. 3 shows a general diagram of an internal combustion engine havingan exhaust gas turbocharger and an electrical auxiliary charger.

FIG. 4 shows an additional flow chart illustrating a control of theinternal combustion engine.

DETAILED DESCRIPTION

In the general diagram shown in FIG. 1, an internal combustion engine 10is illustrated which includes an intake system 12 having a throttlevalve 14, and an exhaust gas system 16. Turbine 18 of an exhaust gasturbocharger is situated in exhaust gas system 16, and the turbine isconnected to compressor 22, which is situated at the intake manifold,via a mechanical connection 20. An electrically actuatable valve 26 isprovided in a bypass duct 24 around turbine 18 of the exhaust gasturbocharger. Various sensors are installed for detecting differentperformance quantities in the region of the internal combustion engine.A selection of these sensors is illustrated in FIG. 1 with a view to theprocedure described below: an air mass flow meter 28, an intake manifoldpressure sensor 30, an engine rotational speed sensor 32, an exhaust gaspressure sensor 34, and an exhaust gas temperature sensor 36. Anelectronic controller 38 is also illustrated which receives lines fromthe above-mentioned sensors: a line 40 from air mass flow meter 28, aline 42 from intake manifold pressure sensor 30, a line 44 fromrotational speed sensor 32, a line 46 from exhaust gas pressure sensor34, and a line 48 from exhaust gas temperature sensor 36. Control unit38 also has an output line 50 used for controlling electricallyactuatable valve 26. In addition to the illustrated input and outputlines, additional input and output lines are provided which arenecessary for controlling the internal combustion engine. These aresymbolized in FIG. 1 by lines 52 through 56 and 58 through 62,respectively, and are not described in greater detail since they are ofonly secondary importance in conjunction with the procedure describedbelow for operating the charger. Input lines 52 through 56 connectcontrol unit 38 to sensors such as lambda probes, temperature sensors,etc., while output lines 58 through 62 lead to injectors, ignitionoutput stages, throttle valve actuators, exhaust gas recirculationvalves, etc.

A procedure is described below which assists in actuating valve 26 aspart of the operation of the exhaust gas turbocharger system. In thepreferred exemplary embodiment, actuating element 26 is a servomotorthat, at the location of the aneroid capsule and the timing valve, movesthe linkage which adjusts the cross section of bypass line 24. However,the procedure described below may also be used in systems having anotheractuator design, such as for electrically actuatable valves, forexample.

The fundamental principle of the procedure is that actuating element 26is actuated depending on the exhaust gas volume flow, thereby creating apilot control for the boost pressure regulation which simulates thecounter-coupling characteristics. In the actual exemplary embodiment,the volume flow of the exhaust gas, at which the setpoint boost pressureis established, is calculated as a function of the engine rotationalspeed and the setpoint boost pressure. In the preferred exemplaryembodiment this is achieved by a characteristics map, in whichparameters are stored which take into account the mechanical andgeometric characteristics of the turbocharger system. The exhaust gasvolume flow produced by the engine is also calculated. This is performedusing a model, for example, in which the exhaust gas temperature isdetermined as a function of air mass flow rate ml (measured by air massflow meter 28) supplied to the internal combustion engine, and theexhaust gas volume flow is determined as a function of the exhaust gaspressure. The difference between the setpoint exhaust gas volume flowand the instantaneous exhaust gas volume flow results in the exhaust gasvolume flow which should pass through the bypass to the turbine. Thisvolume flow is modulated by the output signal from the boost pressureregulator, which is interpreted as a differential volume flow. Thevolume flow calculated from the difference between the setpoint and theactual volume flow, plus that calculated by the boost pressureregulator, is evaluated to determine the position of the electricalactuator. A characteristic line, for example, is provided in which thevolume flow is converted to an actuating signal.

The illustrated pilot control over the exhaust gas volume flow hascounter-coupling characteristics, as the result of which the exhaust gasvolume flow produced by the engine is taken into account. When thesetpoint volume flow is passed through the turbine, the turbinerotational speed increases, and thus the rotational speed of thecompressor situated on the intake side increases as well. This causes anincrease in the boost pressure and the exhaust gas volume flow. Thecalculation and evaluation of the exhaust gas volume flow takes thisinto account in the control, since the pilot control then increases thecross section of the bypass opening. The exhaust gas turbocharger thusremains stable.

The boost pressure regulator itself only performs corrections on astable system. Thus, as a boost pressure regulator it is advantageouslysufficient to use a conventional, robust, and easily usable regulator,such as a regulator having a proportional, integral, and differentialresponse, which is also used for actuators with counter-couplingcharacteristics, as previously mentioned.

The pilot control itself operates in such a way that the cross sectionof the bypass opening is not constant as the exhaust gas volume flowincreases, but instead increases even when the regulator is switchedoff.

The above-described procedure is implemented in the preferred exemplaryembodiment as a program on a microcomputer which is part of control unit38. The program on the microcomputer includes the necessary commands forperforming the procedure.

FIG. 2 shows a flow chart of such a program, the individual blocksrepresenting programs, subprograms, or program steps, in particularcommands or a summation of commands, whereas the connecting linesrepresent the information flow.

First, in 100 a setpoint volume flow VSTUS over the turbine iscalculated as a function of engine rotational speed nmot and setpointboost pressure plsol. In the preferred exemplary embodiment, this iscarried out using a characteristics map, and in another exemplaryembodiment, using calculation steps. Essentially, the setpoint volumeflow will increase with increasing setpoint boost pressure andincreasing rotational speed.

The setpoint boost pressure itself is determined from a setpointpressure ratio between the pressure upstream and the pressure downstreamfrom the compressor, which in turn depends on the engine rotationalspeed. Actual exhaust gas volume flow VSABG is determined in 102. In onepreferred exemplary embodiment, this actual exhaust gas volume flow iscalculated based on supplied air mass ml, exhaust gas temperature Tabg,and exhaust gas back pressure Pabg. The exhaust gas temperature and thesupplied air mass are calculated, whereas the exhaust gas back pressureis measured, or calculated using a model. In the preferred exemplaryembodiment, an equation is used for calculating the actual exhaust gasvolume flow, which is approximately as given below:VSABG=k·ML·TABG/PABGwhere k is a constant.

The difference between setpoint volume flow VSTUS and actual exhaust gasvolume flow VSABG (ΔVS=VSABG−VSTUS) is determined in node 104.Difference ΔVS is sent to an additional node 106.

In addition, a regulating algorithm 108 is provided which determines anoutput variable VSBYST as a function of its input variable. The inputvariable is a difference ΔP which is generated in node 110. In this nodethe setpoint boost pressure and the actual boost pressure PLIST measuredby a boost pressure sensor are compared, and the resulting difference issent to the regulator. The regulating algorithm then generates theoutput variable, which in node 106 corrects pilot control variable ΔVS.The correction is carried out as an addition, for example. In 112 thecorrected pilot control variable ΔVS+VSBYST is converted to an actuatingsignal for the actuator of the exhaust gas turbocharger. In thepreferred exemplary embodiment this is performed using a characteristicsmap, which assigns an output variable τ to the input variable.

A control variable having quantity τ as a parameter is output by themicrocomputer or the control unit for actuating the valve or actuator ofthe charger, which sets a volume flow in the bypass of the turbine. Thisvolume flow corresponds to the volume flow according to the pilotcontrol plus the regulating correction.

In a second exemplary embodiment, the above-described procedure is usedin conjunction with a turbocharger system which in addition to themechanical exhaust gas turbocharger has an electrical auxiliary charger.One such system is illustrated in the general diagram in FIG. 3. Thesystem illustrated in FIG. 1 is supplemented by an auxiliarysupercharger 80, driven by an electric motor, which is situated in thedirection of flow downstream from compressor 22 and upstream fromthrottle valve 14 in the induction tract of internal combustion engine10. This auxiliary supercharger is driven by an electric motor 82 whichis supplied with an actuating signal by controller 38 via an output line84. The other components and lines correspond to those illustrated inFIG. 1, and therefore are provided with the same reference numbers andhave the same function.

One such electrical auxiliary supercharger is connected in series to theexhaust gas turbocharger because of the delayed response characteristicof the exhaust gas turbocharger, and is generally operated whenacceleration is requested. The delayed response characteristic is thuscompensated for during acceleration, and operation is optimized. Theoperating time of the electrical auxiliary charger, which consumesresources of the motor vehicle and in particular greatly increases theload on the battery, should be minimized. It has been shown that thisminimization may be achieved when the electrical compressor isoperating, if the instantaneous exhaust gas volume flow is less than theflow demand of the turbine. These variables are available from theabove-mentioned pilot control. Another criterion for operating theelectrical auxiliary compressor, which may be used in addition to thatdescribed above, is that a setpoint boost pressure is required whichexceeds the base boost pressure. The base boost pressure is the pressurewhich results without special actuation of the exhaust gas turbochargeras a consequence of the air flow to the internal combustion engine.

The auxiliary compressor is operated only until the instantaneousexhaust gas volume flow reaches the flow demand of the turbine. Theoperating time of the auxiliary compressor, and thus the load on thebattery, is thereby minimized. The reason for this is that the exhaustgas turbocharger itself has a co-coupling response. When the volume flowdemand of the turbine is exceeded, the turbine rotates more rapidly, thecompressor rotates with the turbine, and the boost pressure increases.The exhaust gas volume flow increases, which once again results in morerapid rotation of the turbine. As described above, with increasing boostpressure increasingly more exhaust gas must be diverted around theturbine so that the turbine does not overspeed. This is accomplished bythe above-mentioned pilot control, as described above. Thus, if thevolume flow demand of the turbine is met, no auxiliary compression bythe electrical auxiliary compressor is necessary, since the exhaust gasturbocharger then provides sufficient boost pressure through itsco-coupling response.

Thus, suitable measures which specify the operating condition for theelectrical auxiliary compressor are important. This is deduced from theabove-described pilot control of the exhaust gas turbocharger actuator.The exhaust gas volume flow is calculated there from the measured ormodeled variables of air mass flow rate, exhaust gas temperature, andexhaust gas pressure. Likewise, the volume flow demand required forstarting the exhaust gas turbocharger is determined. This is eitherspecified as a fixed value or, as described above, is determined fromthe boost pressure and rotational speed. If the instantaneous exhaustgas volume flow is greater than the flow demand of the turbine, thedifference between the two flows is diverted around the turbine via thewaste gate. Overspeeding of the turbine is thus prevented. However, ifthe volume flow demand of the turbine is greater than the exhaust gasflow delivered, an operating condition for the electrical auxiliarysupercharger is set. The auxiliary compressor is then switched on, andan actuating signal for electrical motor 82 is generated. In this mannerthe exhaust gas mass flow increases, and the turbine starts. When theexhaust gas flow exceeds the flow demand of the turbine by a certainquantity, the auxiliary compressor is switched off again. A switchinghysteresis is advantageously provided here.

In a further exemplary embodiment, the auxiliary compressor is notoperated until, in addition to the operating requirement deduced fromthe exhaust gas flow, there is a requirement for activation of the boostpressure regulation, i.e., when the setpoint boost pressure exceeds thebase boost pressure.

Using the above-described procedure, the auxiliary compressor alwaysswitches off at the same exhaust gas volume flow under various operatingconditions (load, rotational speed, for example). The operating time ofthe auxiliary compressor is optimized.

The procedure described above is implemented here analogously to thefirst exemplary embodiment using a program in the microcomputer ofcontrol unit 38. A flow chart for one such program is outlined in FIG.4. Here as well, the components already described with reference to theflow chart of FIG. 2 are provided with the same reference numbers andhave the function described in FIG. 2.

Thus, in 100 the setpoint volume flow is determined which is eitherspecified by the rotational speed and setpoint boost pressure, or isspecified as a fixed value. This is compared to the exhaust gas volumeflow, which is calculated as above. The difference (ΔVS=VAABG−VSTUS)between the two values represents the volume flow to be diverted via thewaste gate. After correction by the boost pressure regulator in 106,this value is converted to an actuating signal for the actuator of theexhaust gas turbocharger, in particular for the actuator of the bypassvalve.

For activation of the electrical auxiliary supercharger an inverter 200is provided which leads to a switching element 202, which preferablyexhibits hysteresis. If the inverted volume flow ΔVS exceeds thespecified limit, an operating condition signal B_SCEB is generated. Ifthe volume flow falls below an additional threshold, this conditionalsignal is reset. The threshold is selected so that resetting isperformed when the instantaneous exhaust gas volume flow reaches thesetpoint volume flow, or has exceeded it by an amount that is greaterthan a specified quantity. The auxiliary supercharger is thus switchedon when the exhaust gas volume flow is less than the setpoint volumeflow. In addition, in one preferred exemplary embodiment a logical ANDlink 204 is provided in which the conditional signal as described aboveis compared to an additional conditional signal B_LDR. This is set whenboost pressure regulation is requested, i.e., when the setpoint boostpressure exceeds the base boost pressure. If both signals are present, aconditional signal B_SCE is output which results in activation of theelectrical auxiliary charger. This auxiliary supercharger is thenactuated either by a fixed specified actuating signal or, if required,according to the actual boost pressure, air flow, and/or rotationalspeed of the engine, etc.

One preferred exemplary embodiment is illustrated in which thecalculations are made based on the volume flow rates. In anotherembodiment, mass flow rates (exhaust gas mass flow) are used instead ofvolume flow rates.

1-15. (Canceled)
 16. A method for operating at least one supercharger ofan internal combustion engine having a turbine in an exhaust tract ofthe internal combustion engine and at least one compressor in aninduction tract of the internal combustion engine, comprising: providingan actuatable actuating element; and generating an actuating signal forthe actuating element, wherein: the actuating signal is a function of avariable that represents an exhaust gas flow.
 17. The method as recitedin claim 16, wherein: the actuating element one of: controls a crosssection of an opening of a bypass duct around the turbine of an exhaustgas turbocharger, and is an electrical auxiliary charger.
 18. The methodas recited in claim 16, wherein: the variable represents one of anexhaust gas volume flow and an exhaust gas mass flow.
 19. The method asrecited in claim 16, further comprising: calculating an exhaust gasvolume flow based on a supplied air flow, an exhaust gas temperature,and an exhaust gas pressure.
 20. The method as recited in claim 16,further comprising: specifying a setpoint flow; calculating a differencebetween the setpoint flow and an actual flow, the difference yielding adeviation signal; and determining the actuating signal based on thedeviation signal.
 21. The method as recited in claim 20, furthercomprising: one of specifying a setpoint flow as a fixed value anddetermining the setpoint value as a function of performance quantitiesincluding an engine rotational speed and a setpoint boost pressure. 22.The method as recited in claim 21, further comprising: providing a boostpressure regulator that generates an output signal as a function of thesetpoint boost pressure and an actual boost pressure.
 23. The method asrecited in claim 22, further comprising: generating a pilot controlsignal as a function of the exhaust gas flow, wherein: an output signalfrom the boost pressure regulator corrects the pilot control signal. 24.The method as recited in claim 16, further comprising: generating anactivating signal for an auxiliary compressor as a function of theexhaust gas flow.
 25. The method as recited in claim 24, furthercomprising: activating the auxiliary compressor when an exhaust gasvolume flow is less than a setpoint volume flow.
 26. The method asrecited in claim 24, further comprising: activating the auxiliarycompressor when a setpoint boost pressure is greater than a base boostpressure.
 27. The method as recited in claim 24, further comprising:switching off the auxiliary compressor when one of: the exhaust gas flowone of reaches a setpoint flow and exceeds the setpoint flow by aspecified quantity, and a setpoint boost pressure is less than a baseboost pressure.
 28. A method for operating at least one supercharger ofan internal combustion engine having a boost pressure regulator, anoutput signal of the boost pressure regulator generating an actuatingsignal for controlling an actuating element for an exhaust gasturbocharger, the method comprising: providing a pilot control of theactuating element, the pilot control signal being a function of anexhaust gas flow.
 29. A device for operating at least one superchargerof an internal combustion engine, comprising: an electrical control unitthat generates at least one actuating signal for controlling at leastone actuating element of the at least one supercharger, wherein: theelectrical control unit includes an arrangement for determining the atleast one actuating signal as a function of a variable that representsan exhaust gas flow.
 30. A device for operating at least onesupercharger of an internal combustion engine, comprising: an electroniccontrol unit that includes a boost pressure regulator, an output signalof the boost pressure regulator generating an actuating signal forcontrolling an actuating element for an exhaust gas turbocharger,wherein: the electronic control unit includes a pilot control thatdetermines the actuating signal as a function of an exhaust gas flow.